Processed Foods Do Indeed Cause Weight Gain, According To New Study

Have you ever finished eating junk food only to find yourself wanting more junk food? On an intuitive level, it's easy to believe that ultra-processed foods don't fill us up the same way that unprocessed, nutrient-dense ones do. New research published today in Cell Metabolism1 lends some more credibility to the hunch.

Over the course of the two-week study conducted at the National Institutes of Health2, 20 healthy adults were split into two groups. One group was fed a diet of processed meals and snacks while the other one was given an unprocessed diet. Muffins, white bread, sugary yogurts, and diet beverages were some of the items on the processed diet menu while fresh fruits and vegetables, eggs, grilled chicken, fish and beef, whole grains, and nuts and seeds were on the other. (You can see the complete breakdown of what was on everyone's plates here.)

The two menus were formulated to have the same amount of calories, sugar, sodium, and fiber. Participants were told to eat as much of their food as they wanted, and their weight and vitals were closely monitored throughout the study.

At the end of the two weeks, those in the processed diet group consumed 500 more calories a day on average, mostly in the form of carbs and fat. (An interesting aside: People were more likely to eat extra calories at breakfast and lunch than dinner and snacks.) Those who ate the processed diets also gained weight over the course of just two weeks while the other group reported weight loss.

"Limiting consumption of ultra-processed food may be an effective strategy for obesity prevention and treatment," the study concludes.

This result doesn't come as much of a surprise to anyone who's ever stepped on a scale after a weekend of indulging. What's more surprising is the fact that this is the first research to find processed foods do indeed cause weight gain.

"It is important to emphasize that no causal relationship between ultra-processed food consumption and human obesity has yet been established," the study reads. "In fact, there has never been a randomized controlled trial demonstrating any beneficial effects of reducing ultra-processed foods or deleterious effects of increasing ultra-processed foods in the diet." The New York Times reports that those behind the report are planning follow-up studies to explore why the ultra-processed foods had this effect.

As it stands now, processed foods high in sugar, fat, and salt tend to be cheaper (the study's unprocessed meal plan cost 42 percent more than the processed one) and easier to get your hands on. It's part of the reason the majority of the calories3 we consume in America now fall into this weight-gain-promoting category.